1. Field of the Invention
The present invention relates to a device for precise edge alignment of sewing material along a stop straightedge.
A forward edge of the sewing material may be folded over, where it is to be placed along the straightedge. In a feed device, the material is placed on a support and aligned along the straightedge, and then it is grasped by material clamps in a clamping carriage, for being held while sewing operations are carried out.
2.Background Art
A device for aligning sewing material of this general type is known from German Utility Model No. 88 07 378 (corresponding in part to U.S. Pat. No. 4,945,843). (The disclosures of all prior art materials mentioned herein are expressly incorporated by reference.) That known device consists essentially of a table top which serves as support for the sewing material to be used, a stop straightedge arranged on the table top, and four alignment devices arranged on the table top, said devices being entirely identical to each other. Essential parts of each alignment device are a double-acting compressed-air cylinder fastened on the table top as well as an alignment finger made of spring sheet-metal which is fastened to the retractable and extendable piston rod of the compressed-air cylinder. The alignment finger is secured against rotation with respect to its reciprocating movement and is so pivoted that an arcuate hook arranged on the free end of the alignment finger is in a raised position above the table top when the piston rod is extended, while, when the piston rod is retracted, the arcuate hook descends in the direction toward the sewing material until it engages the fold edge of the sewing material toward the end of the movement of retraction. Since the four alignment devices are arranged transverse to the stop straightedge, the material placed on the table top, after the arcuate hooks have acted on the folded edge of the double-folded seam on the sewing material, is pushed against the stop straightedge by the piston rods which retract further into the compressed air cylinders. In this way, a final dependable alignment of the sewing material on the stop straightedge is made possible.
In order to dependably advance the sewing material in the direction toward the stop straightedge for the purpose of edge alignment, it is necessary for the fold edge of the material, for instance a button strip on the front part of a shirt, to be formed by a double-folded seam. The arcuate hook of the alignment finger can dependably act only on such a very pronounced fold edge.
A significant disadvantage of the known device resides in the fact that with single-folded seams, such as on the button strips of the front parts of shirts or blouses, and frequently on buttonhole strips, accurate edge alignment of the material along a stop straightedge is not possible.
Additional background disclosures showing the alignment of sewing material along a stop edge by using a stream of gas in the form of jets of gas or air entering a suction chamber, are found in U.S. Pat. No. 3,886,877 and Germany 33 25 389 C2, which disclose the application of background alignment principles at edge guide devices for workpieces to be sewn.
Federal Republic of Germany OS 23 65 216, corresponding in part to U.S. Pat. No. 3,886,877, discloses providing compressed-air nozzles in cooperation with a material-guide apparatus, the blown air emerging from the nozzles for supporting the movement of the material during its passage through the guide apparatus.